Interest in fuel cell batteries as power sources for portable electronic devices has grown. A fuel cell is an electrochemical cell that uses materials from outside the cell as the active materials for the positive and negative electrode. Because a fuel cell does not have to contain all of the active materials used to generate electricity, the fuel cell can be made with a small volume relative to the amount of electrical energy produced compared to other types of batteries.
Fuel cells can be categorized according to the types of materials used in the positive electrode (cathode) and negative electrode (anode) reactions. One category of fuel cell is a hydrogen fuel cell using hydrogen as the negative electrode active material and oxygen as the positive electrode active material. When such a fuel cell is discharged, hydrogen is oxidized at the negative electrode to produce hydrogen ions and electrons. The hydrogen ions pass through an electrically nonconductive, ion permeable separator and the electrons pass through an external circuit to the positive electrode, where oxygen is reduced.
In some types of hydrogen fuel cells, hydrogen is formed from a fuel supplied to the positive electrode side of the fuel cell, and hydrogen is produced from the supplied fuel. In other types of hydrogen fuel cells, hydrogen gas is supplied to the fuel cell from a source outside the fuel cell. A fuel cell system can include a fuel cell battery, including one or more fuel cells, and a hydrogen source, such as a fuel tank, a hydrogen tank or a hydrogen generator. In some fuel cell systems, the hydrogen source can be replaced after the hydrogen is depleted. Replaceable hydrogen sources can be rechargeable or disposable.
A hydrogen generator uses one or more reactants containing hydrogen that can react to produce hydrogen gas. The reaction can be initiated in various ways, such as hydrolysis and thermolysis. For example, two reactants can produce hydrogen and byproducts. An accelerator and/or a catalyst can be used to increase the rate of reaction or catalyze the reaction. When the reactants react, reaction products including hydrogen gas and byproducts are produced.
Various liquids can be used in hydrogen generators. For example, the liquid can include water that can react with another reactant, or the liquid can include water as one reactant and another reactant dissolved in the water, and the water and the other reactant can react under certain conditions (e.g., when the liquid contacts a catalyst, when the liquid is heated and/or when the pH of the liquid is changed) to produce hydrogen gas.
In one type of hydrogen generator at least one reactant is stored in a reservoir as a liquid, and the liquid is transferred from the reservoir to a reaction chamber, where the liquid or a reactant in the liquid reacts to produce the desired gas. Various means have been used to transfer liquids, including pumps. Pumps can also be used to control the rate of hydrogen gas generation by controlling the rate at which the liquid is transferred.
A hydrogen generator can be part of a system that is at least partially replaceable, so depleted reactants can be easily and economically replaced with fresh reactants. Since hydrogen generating systems can include components that do not have to be replaced at the same time as depleted reactants, it can be advantageous for the hydrogen generator system to include both replaceable components and non-replaceable (i.e., reusable) components. This is especially true when relatively expensive components can be reused.
It is desirable to provide a hydrogen generator system capable of supplying hydrogen gas, particularly to a fuel cell system. It is desirable to provide a hydrogen generator system in which depleted reactants can be easily and economically replaced and in which the number of components that can be reused is maximized. It is further desirable that the hydrogen generator system have excellent reliability, safety, and a simple design that is easily manufactured at a low cost. It is desirable that the hydrogen generator system be highly resistant to leaks, particularly leaks of harmful or corrosive liquids, and highly resistant to malfunctioning due to accumulation of solids in lines, valves and so on.